The four pins
Four pins, three of them wired: GND on the square pad, VCC for the chip, and SIGNAL, which is the chip's own output. NC is connected to nothing. SIGNAL is HIGH while a finger is on the gold pad and LOW the rest of the time, which is what ACTIVE HIGH on the front says.
Three wires and a spare
The header is four right-angle pins, 2.54 mm apart, printed GND, VCC, NC and SIGNAL from left to right with the pad facing you. GND is on the square pad, and that pad is the only way to tell four identical holes apart. Count from it.
Pick a pin to see where it goes. GND is the chip's ground, and also where its two mode pins are soldered. VCC feeds the chip. SIGNAL is the chip's output pin, with the red LED hung off it. NC is in no net at all.
The one to watch is the order. NC sits between VCC and SIGNAL, so a wire one hole short lands on NC, and a pin connected to nothing reads whatever the air around it suggests. That looks exactly like a sensor that never triggers.
What HIGH means
The front prints ACTIVE HIGH beside the header. Touch the pad and SIGNAL goes HIGH; take your finger away and it goes LOW. It does not latch: the chip can be set to toggle on each touch, but this board wires it for plain momentary output, in copper, and there is no jumper to change it. A touch that latches does the toggle in the sketch instead.
VCC is the level SIGNAL reaches
SIGNAL is not a switch to ground or a resistor to a rail. It is the chip's push-pull output, driven from VCC, so HIGH on SIGNAL is the voltage you put on VCC. That makes the wiring rule simple: VCC goes to your board's own logic supply, 3V3 beside an ESP32 or a Pico, 5V beside an Uno. VCC sets the HIGH has the numbers.
When it does not work
The square pad. From the front, pad up and pins pointing down, it is the left-hand pin, and the order is GND, VCC, NC, SIGNAL. The back prints no pin names; turned over, the square pad is on the right and it is still GND.
No. It is soldered to a pad that no trace reaches, so it makes no difference either way. It is there so every TinkerBlock block has the same four-pin header and one cable fits all of them.
No. SIGNAL is driven by the chip in both directions, HIGH when touched and LOW when not, so it never floats while the block has power. Set the pin to plain INPUT. INPUT_PULLUP does no harm to the reading but is not needed.
Yes. Both are misprints on the silkscreen: the chip is the TTP223, and TOCUH is TOUCH. TK43 is the part number, and it matches the box.
Edit this page — content/books/tp223-touch-sensor/the-four-pins.mdx
Questions about this product
See what other owners have asked, and read their solutions.
This page covers several products. Choose yours to see the right discussions.
Discuss this article
Ask about this page. The answer stays here, on the page it belongs to, for whoever hits the same wall next.